Production of sulfur



Aug. 21, 1962 P. URBAN ErAL 3,050,370

PRODUCTION oF SULFUR Filed July 5, 19Go s q. 5 2 E 5 to Q l, 0,/ s

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Pefer Urban By Lesfer 6. Massey A TTOR/VEYS 3,059,370 PRODUCTIGN F SULFUR Peter Urban, Northbrook, and Lester G. Massey, Arlington Heights, Ill., assignors to Universal Dil Products Company, Des Plaines, lli., a corporation of Delaware Filed July 5, 1966, Ser. No. 40,776

6 Claims. (Cl. 23-226) This application is a continuation-in-part of our copending application Serial No.l 554,591 filed December 21, 1955, now abandoned.

This invention relates to a process for the production of sulfur and particularly to a process for producing sulfur from hydrogen sulfide. In addition, the invention also relates to a process for purifying a gas stream by removing hydrogen sulfide from said stream.

ln many industrial processes, large amounts of sulfur are wasted by being vented to the atmosphere as hydrogen suliide. Typical of these are processes for preparing various petroleum products, coking of coal, steel manufacture and others. In many cases, the sulfur is a contaminant inthe ultimate desired product and is converted to hydrogen suliide during processing and disposed of in that form. Besides being wasteful, venting hydrogen sulfide to the atmosphere creates a nuisance which must be abated in many communities to conform with local regulations.

Several solutions to this problem have been put into eect and these mostly have been used to abate the nuisance rather than to conserve sulfur. The processes are usually difficult to effect and rather costly and usually consist of converting the hydrogen sulfide to sulfur or sulfuric acid or some other salable form. One such solution has been to separate the hydrogen sulde from the main stream by such means Aas an absorber employing an alkaline liquid such as an amine or metal hydroxide solutions in countercurrent contact with the hydrogen sulfide containing gas. The absorbing liquid is then stripped of H28 and H2S ispartially burned to form SO2 and Water and the remaining H2S is reacted with the SO2 to produce sulfur and water. rille reaction is eected at high temperatures employing a heterogeneous catalyst such as bauxite and preferably at high pressure. This method has many unsatisfactory features including the expense and diculty of concentrating H28 by means of an alkaline solution with subsequent stripping, the use of heterogeneous catalysts which are not too well suited to chemical processes resulting in solid products, the difculty of using corrosive materials such as water-SO2 mixtures at high emperatures and, in fact, the diihculty of employing high temperatures. It is an object of this invention to provide a novel process for recovering substantially pure sulfur from a gas stream containing H28 or mercaptans. Because of the great abundance of H28 containing gas streams, this invention will be described primarily in relation to this particular compound. The process of this invention overcomes the diiculties hereinbefore enumerated by providing a simple, liquid phase, low temperature, non-catalytic process which results in large conversions of hydrogen sulde to substantially pure sulfur.

One embodiment of this invention resides in a process for the production of sulfur which comprises absorbing sulfur dioxide and hydrogen sulfide in a solvent comprising an ester and having from about 0.5% to about 40% by volume of water dissolved therein, reacting the sulfur dioxide and hydrogen suide in contact with said solvent, thereby forming sulfur, and separating the sulfur from said solvent.

A specic embodiment of the invention is found in a process for the production of sulfur which comprises absorbing sulfur dioxide and hydrogen sulide in a solvent comprising methyl acetate, and having from about 0.5%

states arent mice to about 40% by volume of water dissolved therein, reacting the sulfur dioxide and hydrogen sulfide in Ycontact with said methyl acetate, thereby forming sulfur and separating the sulfur from said solvent.

Other objects and embodiments referring to alternative organic esters will be found in the following further detailed description of the invention.

Briefly, the process of this invention provides for effecting the reaction between sulfur dioxide and hydrogen suliide to form sulfur and water while these two reactants are absorbed in a common liquid medium. By providing for such solution or absorption, the molecules are apparently brought into close proximity with others so that reactions can occur more readily between them. In the process of this invention, the reaction occurs without a catalyst substantially to completion even at ambient temperatures in contrast to the process employing a vapor phase which requires high temperatures and a catalyst and which results in low conversions compared with'the present process.

The solvent employed in this invention must have certain characteristics. Since a certain amount of water is required for the reaction to proceed rapidly, as will be hereinafter demonstrated, water must necessarily be soluble in the solvent to some significant extent. Another characteristic is that the solvent must be capable of absorbing or dissolving both hydrogen suliide and sulfur dioxide. Another requirement of the solvent, although one that is easily met, is that it must not dissolve large quantities of sulfur inasmuch as a solvent having this characteristic would introduce another step in the process, namely recovering dissolved sulfur from the solvent.

Two distinct types of solvent may be used. The first is a solvent miscible in all proportions with water and when such a soivent is used, means must be provided to remove excess water from the solvent so that too muchV dilution does not occur. The other type of solvent is one which `dissolves only limited quantities of water. A solvent with limited miscibility with water, to be used in this invention, must be capable of dissolving the necessary quantities of water to be hereinafter described and preferably is saturated Within the desired water concentration range. When such a solvent is used, the excess Water which results from the reaction may be removed simply by drawing oit the aqueous phase.

It has now been discovered that not all organic solvents are suitable for the production of sulfur, certain oxygenated organic compounds such as the glycols although effective in some respects in forming sulfur possess the disadvantage of having the sulfurthus formed in a ilocculent or tacky state which is diiiicult to recover b-y the commercial methods of separation. The sulfur formed by the use of glycols as the solvent in this process is diiiicult to separate by filtration. For example, solutions of sulfur suspended in diethylene glycol or triethylene glycol when subjected to iiltration resulted in either the solutions passing through a iilter without leaving any sulfur or, after a period of time, said suspensions would clog the iilter completely before any substantial amount of solution had passed through. However, in contradistinction to this, We have now discovered that when certain organic compounds such as organic esters -are utilized as the organic solvent in the process of this invention, the sulfur which is produced is crystalline in `form as contrasted to the amorphous form of sulfur produced by glycols are used as solvents. The sulfur crystals formed when using an organic ester as the organic solvent are large and readily iilterable, whereas the sulfur crystals,A when using glycols as the organic solvent, form into some `type of gelatinous, compressible mass.- However, this mass is tacky in contrast to the hard crystals hereinbefore set forth and thus cannot be readily filtered.

methyl Aprc`rpio`na-te, 1 ethyl propionate, propyl'propionatq butyl propionate, methyl butanoate, ethyl butanoate, etc.

The process of this invention maybe best described with reference to the accompanying drawing which is intended toV be illustrative of the invention rather than limiting on its broad scope. v Y t "In the drawing, H28 or HZS-containinggas from any Vsourcersuch as those hereinbefore described is introduced n -through line 2, into the lower portion of absorber 1. This gasmay be, for example, the normally gaseous material .in the effluent from a petroleum desulfurization or reformingV process,n in which case it is desirable to recirculate the hydrogen in the gas, but to remove the hydrogen sulfide c from it since hydrogen sulde has an adverse effect upon the catalysts employed in such process. in absorber '1, the rising hydrogen 'sulfide is mixed with SO2 which is intros duced inthe lower portion of absorber 1 through line 3 and the mixture is contacted lwith a descending watercontaining organic ester stream. Absorber 1' will contain internal means-for effecting intimate contact between a rising gas stream and ya descending liquid stream such as, but not limited to, perforated plates, bubble cap plates, turbo-V grid trays, packing, screens or any other conventional devicefor causing such contact. The ester in this embodiment'is introduced into the upper portion of absorber 1 Y Y through line Stand is obtained as will be hereinafter dis-V cussed. Y Y

" may, however, separate more water from the solvent than invention preferably contains from about 10.0% to about hydrogen sulfide-free gas stream discharging from the top of absorber 1 through line 4. This not only is conservative of ester but preventsadverse effects which such solvent might have as an impurity in the gas stream.

As the ester and water descend through absorber 1 they absorb hydrogen sulde and sulfur dioxide. The'ester and water'are'maintained at a temperature of from about 0 to about 120- C. or higher and preferably lfrom about 20, to about 100 C. The only temperature limitation on this process is that the temperature must be such as to have a liquid phase solvent at absorber conditions.

When maintained at these conditions, the absorbed hy- Y of -a suitable solvent and optimum operating conditions willcause substantially complete reaction of hydrogen sulde with sulfur dioxide so that then residual unreacted components in the stream discharging vfrom absorber 1 will be negligible. The material passing through line 5 methyl acetate.

' is added to each of the methyl acetate portions to bring oxide is added to one aliquot of each water concentrapasses to sulfur removal zone 6 wherein the sulfur is Y removed from the stream and thereafter passed out to a recovery zone', not shown, through Vline 12. When the sulfur product Vis solid, it may be removed by ltration, centrifugally, 4by settling or any other known means of removing solid particles from `a liquid. vThe sulfur may be removed as a liquid when the Vsulfur removal zone is at a suiciently high temperature, in which case it may simply be drawn off from the total liquid as a separate immisci'ble phase.

The sulfur-free liquid passes through line 7 to water separator 8 wherein the water formed in the reaction of H28 with SOZiis removed to prevent a build-up of water in the circulating solvent stream. Water separator 8 may vconsist merely of Va settling zone when the solvent ernployed dissolves only limited quantities of water. VWhen Ldifferent vwater concentrations Vfor a period of timefof 4 Y Y Y then water removal zone 8 must separate water from the solvent by some other means such as fractionation, evapoA ration, hydration of salts, etc.l Water separator 8 may separate water only to the extent that it was added by the reaction in which case water will be withdrawn'through lines 10 and 11 and the desired water-solvent mixture will pass to the top Yof absorber 1 via line 9. Water separator 8`V what was Vadded by the reaction in which case'some water is withdrawn via'rline 11 but some is added to the upper Y portion of absorber 1 via line 10 to scrub'solvent from the '7* exit gas as hereinbefore' described. Y Y As will behereinafter demonstrated, the solvent of this 40% by volume offwater. It is preferred that the solvent employed have limited water solubility but it must dissolve at least 0.5% and preferably not'more than 40% waterat the temperature conditions in absorber 2. iAs hereinbefore stated, an organic ester having these char# acteristics may conveniently kbe used since Vwater of re-l action can be separated by settling and an elaborate fractionation zone is not required. Y

In addition to the continuous process hereirnbefore described theprocess of this invention may also be effected Y in a batch type operation. When a batch' type operation is used the desired ester and the water are placed in an appropriate apparatus following which the sulfur dioxide and hydrogen sulfide are then bubbled through the solution. After a predetermined period ofY time has elapsed the solution containing the crystalline sulfur is then subjected to ltration whereby the sulfur is sepa` rated from the ester and water.

The following examples are given to illustrate Vthe process of the present invention which, however, are not'in, tended to limit the generally broad scope of the present Yinvention in strict accordance'there'with.

Example I In this example the solvent which is utilized comprises.V

A predetermined amount of methyl acetate is divided into three separate portions and water the solvent to the desired water content, the resultingY solutions containing 10%, 20% and 30% by volume of water, respectively. Following this each portion of the solvent is then divided into ktwo aliquots and sulfur di! tion by bubbling Vthe gas therethrough for a period of Y about 5 minutes. Hydrogen sulfide gas is bubbled'into the other aliquot of the preselected solvent containing from about l0 to about 20 minutes'. This longer time for absorption of hydrogen sulde is due to the'fact that the solubility of hydrogen sulfide in the solvents is much less than'that of sulfur dioxide. Following this the concentration of the sulfur dioxide in one aliquotand the concentration of hydrogen sulfide in the other aliquot portion is determinedv by Viodine-titration and iodine thiosulfate titration, respectively. Y

The two aliquots of each of the different water con-V centrations are combined in graduated V'cylinders and the formationof sulfur therefrom is observed. It will be Y noted that sulfur will precipitate out in a crystalline form in .each of the cylindersiwithin a relatively short period of time. Y Y

At the same time a similar experiment utilizing triethyltin,

Y ene glycol containing from about 2-6% water is performed in a similar manner, that is, triethylene glycol t 1s divided into two aliquots, one'aliquot having sulfur dioxide gas bubbled therethrough while the other portion has hydrogen sulfide gas bubbled therethrough, The Y two aliquot portions are then combined and mixed. The sulfur formed in the triethylene glycol will still remain v1n a suspended state for a period of time identical to' that in which the sulfur in the methyl acetate solution as precipitated out in a crystalline form.

Example II organic ester which is used in this example comanhydrous ethyl acetate. The ethyl acetate is div to. three portions and water added thereto so that alsolution contains 20% and 30% water by olumefrespectively. Each of the three solutions is ydi- 'de'dfinto two aliquot portions. Sulfur dioxide gas is ubbledthrough one of the aliquot portions while hydroensulde gas is bubbled through the other. The two nrtznjlfare combined and mixed thereby causing the ormationof sulfur. The sulfur will precipitate in a ucrystallinei form within a relatively short period of time 'dfis easily separable from the solution by conventional -such as ltration.

Example III Methyl'propionate is treated with water so that three portions will contain 10%, 20% and 30%, respectively. Each of the water-methyl propionate solutions is divided into two 'aliquot portions, one portion having sulfur dioxide gas bubbled therethrough while the other portion has hydrogen sulde gas bubbled therethrough. After completion of the addition of sulfur dioxide and hydrogen sulfide to the aliquot said aliquot in each water concentration range is combined. The sulfur thus produced will precipitate in a crystalline state in each of the solutions within a relatively short period of time and will be easily separable by filtration.

Example IV In this experiment anhydrous ethyl propionate is treated in a manner similar to that set forth in the above example, that is, three solutions containing 10%, 20%

and 30% by volume of water, respectively, are prepared. I

Each of these water-ethyl propionate solutions are divided into two aliquot portions and are treated with hydrogen suliide gas and sulfur dioxide gas. After completion of the gas addition the two portions in each water vrange are combined and mixed. The sulfur thus produced will precipitate in a crystalline form and will be easily separable by filtration.

Example V 6 above examples precipitate in a crystalline form and will be easily separable by conventional means such as iiltration.

We claim as our invention:

l. A process for the production of sulfur which comprises absorbing sulfur dioxide and hydrogen sulfide in a solvent comprising an ester, and having from about 0.5% to about 40% by volume of water dissolved therein, reacting the sulfur dioxide and hydrogen sulfide in contact with said ester, thereby forming sulfur, and separating the sulfur from said solvent.

2. A process for the production of sulfur which comprises absorbing sulfur dioxide and hydrogen sulfide in a solvent comprising methyl acetate, and having from about 0.5 to about 40% by volume of water dissolved therein, reacting the sulfur dioxide and hydrogen sulfide in contact with said methyl acetate, thereby forming sulfur and separating the sulfur from said said solvent.

3. A process for the production of sulfur which comprises absorbing sulfur dioxide and hydrogen sulfide in a solvent comprising ethyl acetate, and having from about 0.5% to about 40% by volume of water dissolved therein, reacting the sulfur dioxide and hydrogen suliide in contact with said ethyl acetate, thereby forming sulfur and separating the sulfur from said solvent.

4. A process for the production of sulfur which comprises absorbing sulfur dioxide and hydrogen sulde in a solvent comprising methyl propionate, and having from about 0.5% to about 40% by volume of water dissolved therein, reacting the sulfur dioxide and hydrogen sulfide in contact with said methyl propionate, thereby forming sulfur and separating the sulfur from said solvent.

5. A process for the production of sulfur which comprises absorbing sulfur dioxide and hydrogen sulde in a solvent comprising ethyl propionate, and having from .about 0.5% to about 40% by volume of water dissolved therein, reacting the sulfur dioxide and hydrogen suliide in contact with said ethyl propionate, thereby forming sulfur and separating the sulfur from said solvent.

6. A process for the production of sulfur which comprises absorbing sulfur dioxide and hydrogen sulfide in a solvent comprising propyl acetate, and having from about 0.5 to about 40% by volume of water dissolved therein, reacting the sulfur dioxide and hydrogen sulde in contact with said propyl acetate, thereby forming sulfur and separating the sulfur from said solvent.

References Cited in the file of this patent UNITED STATES PATENTS 2,881,047 Townsend Apr. 7, 1959 FOREIGN PATENTS 734,577 Great Britain Aug. 3, 1955 

1. A PROCESS FOR THE PRODUCTION OF SULFUR WHICH COMPRISES ABSROBING SULFUR DIOXIDE AND HYDROGEN SULFIDE IN SA SOLVENT COMPRISING AN ESTER, AND HAVING FROM ABOUT 0.5% TO ABOUT 40% BY VOLUME OF WATER DISSOLVED THEREIN, REACTING THE SULFUR DIOXIDE AND HYDROGEN SULFIDE IN CONTACT WITH SAID ESTER, THEREBY FORMING SULFUR, AND SEPARATING THE SULFUR FROM SAID SOLVENT. 